The present invention is directed in general to calibration techniques, and in particular to a method of calibrating a bulk material metering conveyor of the gravimetric or material weighing type that provides a continuous periodic pulse signal whose frequency is indicative of the feed rate (net weight per unit of time) of the material carried by the belt.
In such a conveyor, a piezoelectric type or strain gauge type load cell transducer supports a weighing roller having the conveyor belt riding on it to provide, for a known weighing span increment of belt length, a gross weight signal indicative of the weight of material on the belt plus the tare weight, i.e., the weight of the belt section (weighing span) supporting the material, the weight of the weighing roller, and the weight of other load cell-supported elements. The conveyor further includes a belt speed transducer such as a belt drive shaft encoder of the electronic odometer type providing a pulse for each increment of belt travel, the rate of such pulses constituting a belt speed signal (belt length increments per unit of time) that is multiplied by a tare-adjusted weight signal (net weight per belt length increment) to provide a product signal indicative of the feed rate (net weight per unit of time) of the material being metered by the conveyor. The product signal is then converted into a periodic pulse signal whose frequency is indicative of the conveyed material feed rate. For example, in the case of a metering conveyor used to feed coal to a fossil fuel power plant boiler or metal ore to a furnace, a feed rate signal frequency range of 100 Hertz to 10 Kilohertz could represent a feed rate range of minimal tons of material per hour to 100 tons of material per hour. Also, the feed rate signal can be integrated to indicate the total or cumulative amount of material delivered by the conveyor.
To ensure the accuracy of the feed rate signal and other values calculated from it, it is necessary from time to time to calibrate the tare weight compensation used to adjust the gross weight signal. It is also desirable to calibrate the gross weight signal from the load cell and the belt speed signal from the shaft encoder. In effecting such feed rate signal calibration, it is desirable to minimize the amount of calibration equipment needed, the amount of time it takes to calibrate the feed rate signal, and the complexity of the calibration procedure.